STRFNFCA datasheet(13/74 Pages) STMICROELECTRONICS

13 / 74 page

STRFNFCA

Communication protocols

Doc ID 023077 Rev 10

13/74

Figure 10.

Reading data from STRFNFCA

Data must be sampled at the rising edge of the SCK signal.

‘Sending’, ‘Polling’ and ‘Reading’ commands must be separated by a high level of the

SPI_SS line. For example, when the application needs to wait for data from the STRFNFCA,

it asserts the SPI_SS line low and issues a ‘Polling’ command. Keeping the SPI_SS line low,

the Host can read the Flags Waiting bit which indicates that the STRFNFCA can be read.

Then, the application has to assert the SPI_SS line high to finish the polling command. The

Host asserts the SPI_SS line low and issues a ‘Reading’ command to read data. When all

data is read, the application asserts the SPI_SS line high.

The application is not obliged to keep reading Flags using the Polling command until the

STRFNFCA is ready in one command. It can issue as many 'Polling' commands as

necessary. For example, the application asserts SPI_SS low, issues 'Polling' commands and

reads Flags. If the STRFNFCA is not ready, the application can assert SPI_SS high and

continue its algorithm (measuring temperature, communication with something else). Then,

the application can assert SPI_SS low again and again issue 'Polling' commands, and so

on, as many times as necessary, until the STRFNFCA is ready.

Note that at the beginning of communication, the application does not need to check flags to

start transmission. The STRFNFCA is assumed to be ready to receive a command from the

application.

Figure 11.

Reset the STRFNFCA

To reset the STRFNFCA using the SPI, the application sends the SPI Reset command

(Control Byte 01, see Figure 11) which starts the internal controller reset process and puts

the STRFNFCA into Power-up state. The STRFNFCA will wake up when pin IRQ_IN goes

low. The STRFNFCA reset process only starts when the SPI_SS pin returns to high level.

Caution:

SPI communication is MSB first.

Table 5.

Interpretation of flags

Bit

Meaning (Application point of view)

[7:4]

Not significant

Data can be read from the STRFNFCA when set.

Data can be sent to the STRFNFCA when set.

[1:0]

Not significant

MOSI

0 0 0 0 0 0 1 0

X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X

Control Byte

MISO

X X X X X X X X

Resp Code

LEN

DATA

Several data bytes

MOSI

0 0 0 0 0 0 0 1

Control Byte 01

MISO

X X X X X X X X

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